Heatsinks: Considerations, guidance, and best practices.

Heatsinks

Why do we need a Heatsink?

If any heat source in an electronic device cannot be cooled efficiently through conduction or convection, then a heatsink is required to move the heat away from the heat source so that conduction or convection is more evenly managed. Heat generation is one of the most important challenges for electronic devices since it affects the device’s reliability. It is mainly generated from the flow of electrical current through various components in a circuit, such as integrated circuits, transistors, and other electronic components. The primary cause of heat generation in electronic circuits is electronic resistance to the current flow. So, efficient thermal management frameworks are essential to avoid overheating, ensuring a long lifecycle and optimal safety of the electronic devices. [1]

Consequences of Overheating

When a device overheats, it can lead to performance issues, unexpected shutdowns, and even permanent damage to the inside components. There are several techniques for cooling, including different styles of heatsinks, thermoelectric coolers, forced air systems, fans, and heat channels. In power electronics, cooling systems must evacuate excess heat to maintain reliability and power density. So, electronic components should always operate within their rated operating temperature range, the safe operating area (SOA).  [2]

Overheating can happen for different reasons, including intemperate utilization, poor ventilation, and defective cooling systems. Extreme heat can slow and even damage devices [3].

Working Principle and Concept

Heatsinks operate on the fundamental principle that heat transfer from a hot to a cool region is proportional to the available surface area, as governed by the second law of thermodynamics. Heatsinks conduct heat away from critical electronic components, maintaining them within their rated operating temperature range. The absorbed heat is then removed through natural or forced air convection.

Heatsinks function either passively through natural convection or actively using mechanisms like fans or liquid cooling to improve heat dissipation. Key performance factors for heatsink design include:

Optimizing these parameters will enhance heat exchange efficiency or thermal conductivity, resulting improvement of heat transfer coefficient.

Active and Passive Heatsink

Heatsinks are classified into passive and active cooling methods. Passive cooling relies on natural convection and radiation for heat dissipation without external assistance. On the other hand, active cooling employs external devices like fans, pumps, or thermoelectric coolers (TECs) to boost heat transfer and cooling efficiency. The choice of a heatsink is determined by the necessary resistance to meet component thermal requirements with active solutions such as forced air or liquid cooling offering tailored thermal management solutions at different levels. (See Fig. 1) [5]

Types of Heatsink by Design

Heatsinks are classified into passive and active cooling methods. Passive cooling relies on natural convection and radiation for heat dissipation without external assistance. On the other hand, active cooling employs external devices like fans, pumps, or thermoelectric coolers (TECs) to boost heat transfer and cooling efficiency. The choice of a heatsink is determined by the necessary resistance to meet component thermal requirements with active solutions such as forced air or liquid cooling offering tailored thermal management solutions at different levels. (See Fig. 1) [5]

Types of Heatsink Based on Manufacturing

Design Optimization

To enhance the thermal performance of heatsinks in both natural and forced convection, various design optimization strategies can be used. Like optimizing fin designs such as trapezoidal, curved, and angled fins can improve heat transfer efficiency, adding a cover plate over straight fins can improve the chimney effect, resulting in more heat transfer. In forced convection, adding internal flow channels can be used to design high-performance heatsinks with efficient heat dissipation capabilities.

Fin efficiency depends on length, thickness, thermal conductivity, and heat transfer coefficient.

Common heatsinks have a fin aspect ratio between 3:1 and 5:1. In forced convection applications, efficiency should be within the 40 to 70 % range. Also, expansion of the surface area, precise fin design, material choice, and an integrated thermal management system are the factors that improve the performance of a heatsink

Parametric Approach to Optimize Heatsink Design

To optimize the relationship between design intent and design response:

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1. 01Optimal fin spacing and number of fins are crucial for maximum heat transfer. Thinner fins improve performance by allowing more fins per base plate, while fin height and length significantly affect heatsink conductance and temperature regulation. The results indicate that careful consideration of fin dimensions can lead to an efficient heatsink design that meets specific thermal performance requirements [8]

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1. 02Perforated pinned heatsinks improve CPU temperature, fan power consumption, heat transfer rate, and positioning of perforations plays a significant role. Perforated heatsinks are lighter and more efficient for cooling electronic devices and systems [10].

General Rules

These general rules apply to heatsinks:

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1. 01Thermal interface materials (TIMs) play a critical role in efficient heat transfer. TIMs bridge microscopic gaps and imperfections between mating surfaces, ensuring a low-resistance thermal pathway for heat dissipation. Use TIM to enhance thermal conductivity.

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1. 02Mount fins in the vertical plane for optimum natural convective cooling. Do not overcrowd or obstruct devices.

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1. 03Do not block airflow around heatsinks, particularly directly above and below items that rely on natural convection.

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1. 04If thermal demands are particularly high, consider using forced convection.

Recommended Heatsink Materials

The most frequent materials used in the construction of heatsinks are those with high thermal conductivity.

Selecting the Right Heatsink

Selecting the right heatsink is based on for key considerations:

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1. 01Determine Heat Generation: Calculate the amount of heat, Q, generated by the device in watts (W).

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1. 02Device & Ambient Temperatures: Identify maximum junction temperature and ambient air temperature.

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1. 03Convection Type: Identify whether cooling is natural or forced. For forced convection, know air flow velocity (LFM).

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1. 04Calculate Thermal Resistance: Thermal Resistance = (Tj - Ta) / Q

Once you have calculated the required thermal resistance, you can select a heatsink that can handle this thermal load and maintain the device within its safe operating temperature range. The choice of heatsink will depend on factors like material, fin design, and whether it uses natural or forced convection. Remember to consider the thermal interface materials and their resistivity values as well.

General Recommendations

Our general recommendations are summarized below

Conclusion

Heatsinks maintain optimal operating temperatures, prevent overheating, and ensure the reliability of electronic devices. Heatsink design works on the principle of heat transfer, where the surface area available for conduction or convection influences the amount of heat dissipated. The fabrication of heatsinks is different, with different types of designs like pin fin, plate-fin, and stacked fin heatsinks tailored for specific applications and cooling requirements. Active and passive cooling methods are employed, utilizing natural or forced convection to dissipate heat effectively. Design optimization strategies, such as fin geometry and thermal interface materials, are crucial for enhancing heatsink performance.

Materials like aluminum, copper, heat pipes, graphite, and ceramics are commonly used for their high thermal conductivity. Selecting the right heatsink for a specific application involves calculating heat generation, determining device and ambient temperatures, identifying the convection type, and calculating thermal resistance to ensure that the device will operate within safe temperature limits. Heatsinks are indispensable components in electronics, ensuring efficient heat dissipation and optimal device performance.

About Whizz Systems

Whizz Systems is an end-to-end Electronics Manufacturing Services firm. We specialize in Electronic Design and Manufacturing with an emphasis on NPI. We are based in Silicon Valley, and can smoothly transition projects to our new high-volume facility in Malaysia.

With over 30 years of experience, we have extensive experience supporting major companies like Xllinx, Amazon, Google as well as startups you may or may not have heard of to get their products to market.

Learn more: email us at sales@whizzsystems.com to connect with our team of industry experts about your projects today.

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1. 01Heat Generation by Electrical Current in a Quantum Dot Hybridized to Majorana Nanowires

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1. 02Synthetic Jet-Based Hybrid Heatsink for Electronic Cooling

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1. 03The Effects of Heat on Electronic Components

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1. 04Heatsinks

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1. 05Electronic device with integrated passive and active cooling

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1. 06Heat Sink Manufacturing Guide